TPS65218D0: Coin cell discharging

David Park

Expert 5670 points

Part Number: TPS65218D0
Other Parts Discussed in Thread: AM3358,

Hi,

Customer is designing AM3358+TPS65218D0 for battery backup supply.

There is fast discharging issue of coin cell battery.

You can see green box in attached file for checking supply by coin cell

- VDDS_RTC of AM3358

- EXT_WAKEUP, RTC_PORZn

Could you review the schematic and check why there is fast discharging of coin cell?

TPS65218D0RSLR AM3358_RTC(DCDC6).pdf

Thanks.

7 months ago

0 James Steenbock 7 months ago

TI__Genius 17995 points

HI David,

Just to clarify the issue, you are seeing coin cell battery voltage discharging faster than expected?

Regards,

James

0 Ki-Yong Han 6 months ago in reply to James Steenbock

Prodigy 60 points

That's right. Is there a way to slow down the coin cell battery discharge?

0 James Steenbock 6 months ago in reply to Ki-Yong Han

TI__Genius 17995 points

Hi Ki-Yong,

In the datasheet, the CC pin is connected to the battery through a 10 Ohm resistor. This may slow the battery discharge a bit but I don't know if that's the source of your discharge issue. If possible I would double check to make sure that there's aren't any unexpected current draws on the CC battery.

Below is some power path impedance information from the CC pin. Depending on the impedance and leakage current you should be able to tell whether the current draw on your CC battery is expected or abnormal.

It looks like VRTC is connected to the CC battery in addition to the PMIC connection. If VRTC is an output from the CC battery, this may be sapping the charge.